Let's start with the facts- Muramasa was released by relatively small publisher Ignition on Sept 8th and cost $50 new, Spyborgs was released by relatively big publisher Capcom on Sept 25th and cost $40, and Dead Space: Extraction was released by super-huge publisher EA on Sept 29th and cost $50. Muramasa reportedly sold approximately 35K in Sept, while Spyborgs sold around 500 units total that month. Dead Space: Extraction put in  around 9K.

Not a fair "fight" by any means, but one could argue that in the grand scheme, the advantages and disadvantages between the three games more or less balanced out. Muramasa got a three week head start, but it's an original IP in "dead" genre (2D action-platformers). Spyborgs is also a new IP, but it cost ten dollars less than Muramasa, and had Capcom's muscle behind it from the start. Dead Space Extraction had the most going for it; an established IP, tons of positive press, and a publishing giant like EA to back it up. 

So why did Muramasa sell more than the other guys?

I'd like to say that it's because the "hardcore" Wii owner values unique, "off beat" experiences, and has a great respect for 2D gaming. More than likely though, it's just because Muramasa has better boobs.

[Via GoNintendo]